The coupling of mass spectrometers with liquid chromatography systems has provided a very valuable tool for identifying organic compounds. The unique value of the liquid chromatographic separation systems is their ability to separate solutions containing mixtures of organic compounds into liquid fractions containing individual compounds. However, the product of the liquid chromatographic column is an eluant liquid solution of the compound or compounds to be analyzed at atmospheric pressure. The mass spectrometer analyzes compounds in a high vacuum system. Evaporation of the eluant solvent and presentation of the desolvated particles to the ionization chamber of the mass spectrometer in a suitable form for ionization has presented serious difficulties limiting the sensitivity of the mass spectrometer and greatly complicating its efficient operation. The high vacuum required in the ionization chamber cannot be achieved in the presence of a significant quantity of residual solvent liquid. Therefore, efficient solvent separation and isolation of the desolvated particles are critical for optimum mass spectrometry operation.
The early systems relied upon the vacuum expansion to reduce the relative proportions of non-volatile component to solvent component passed to the ion chamber. U.S. Pat. No. 3,997,298 describes a system wherein eluant liquid is injected from a capillary tube into a vacuum chamber, and the gaseous products are passed directly to the ion chamber. In a similar approach, the system described in U.S. Pat. No. 4,647,772 atomizes a liquid sample in a vacuum chamber, and the gaseous products are passed through an aperture opening leading to the ionization chamber; the conical aperture has an axis perpendicular to the direction of flow of gases through the vacuum chamber. U.S. Pat. No. 4,730,111 and Vestal, M. International Journal of Mass Spectrometry and Ion Physics. 46:193-196 describe similar systems wherein heat is supplied to assist in the evaporation of the solvent. The amount of solvent passed to the ion chamber by these systems is undesirably high for most effective operation of the mass spectrometer.